Super Mario 128

If you were looking for the Event Match from Super Smash Bros. Melee, see here.

A screenshot from an early demo.

Super Mario 128 is the name of a series of projects by Nintendo to create a sequel to Super Mario 64. The project experimented with new technology and ideas to incorporate into later games. A demo of the project was released by Nintendo. The demo featured one hundred twenty-eight Marios on screen at once. Other features of the demo included the use of "rapid generation", later seen in the game Pikmin, and "sphere walking", seen in the The Legend of Zelda: Twilight Princess and Super Mario Galaxy. Some confuse Super Mario 128 with Super Mario Galaxy, a game that incorporates the experiments from the Super Mario 128 project. However, Super Mario Galaxy may be the culmination of the project's work, as Super Mario 128 sought to create an innovative sequel to Super Mario 64. Super Mario 128 could now be seen as Super Mario Sunshine or Super Mario Galaxy.

During his keynote speech at the Game Developers Conference 2007, Shigeru Miyamoto revealed what eventually happened to Super Mario 128. "What happened to Mario 128?" said Miyamoto at the end of his keynote, "most of you already played it...," then the screen showed that Mario 128 equaled Pikmin.

Trivia

Super Smash Bros. Melee features an Event Match called "Super Mario 128" (Event Match #22). In this event, the fighter must defeat 128 tiny Marios.
It is most likely that the game was named Super Mario 128 because 128 is double of 64, as the game was thought to be a sequel to Super Mario 64.